Stabilized transistor regulator



Aug. 1, 1967 P. W. USSERY STABILIZED TRANSISTOR REGULATOR Filed May 15,1964 United States Patent ABSTRACT OF THE DISCLOSURE A negative lineregulator wherein a p-n-p transistor connected with its emitterelectrode facing the load is employed as the variable impedanceregulating element. Absolute stability against input source variationsis provided by serially connecting a zener diode with the baseemitterpath of the regulating transistor and the collectoremitter path of theamplifier transistor.

This invention relates to voltage regulator circuits and moreparticularly to transistor voltage regulator circuits with a high degreeof stability.

In the more common regulator circuits, the emittercollector path of aregulating transistor, which acts as a variable impedance, is connectedbetween the input source of unregulated potential and the load. Loadvoltage variations are detected and compared with a reference voltage byan error-detector stage, the output of which is connected through astage of amplification to control the bias of the base emitter path ofthe regulating transistor. The impedance of the collector-emitter pathof the regulating transistor is thus controlled in accordance with loadvolt-age variations.

Because of its high power capabilities and commercial availability, ap-n-p transistor is generally used as the regulating transistor. Whenthe emitter-collector path of the p-n-p transistor is connected betweenthe positive terminal of the source and the positive terminal of theload in positive line regulator fashion, degeneration due to inputvoltage variations generally presents no problem. When theemitter-collector path of the p-n-p regulating transistor is connectedbetween the negative terminal of the source and the negative terminal ofthe load to form a negative line regulator, however, input voltagevariations interfere with the operation of the amplifier and therebydistort the error or load voltage variation signal and interfere withthe regulating property of the circuit. To eliminate this degeneration,the circuits of the prior art have often substituted n-p-n transistorsfor the p-n-p regulating transistors. Since n-p-n transistors withhigher power capabilities are not readily available commercially,however, this method is not entirely satisfactory.

Notwithstanding the degeneration problem, both positive and negativeline regulators have suffered transistor damage and failure due to hightransient voltages in excess of maximum inverse voltage ratings of theregulator transistors. To protect against such transients, theregulators of the prior art have generally chosen transistors withmaximum inverse emitter-base and collector-emitter voltage ratings inexcess of the largest transient voltages expected. Such components,however, tend to be expensive and considerably increase the circuitcost.

It is therefore an object of this invention to provide a voltageregulator that is insensitive to input voltage variations and uses apn-p transistor as the regulating element.

It is a further object of the invention to provide a voltage regulatorwherein transistors with relatively low inverse voltage ratings areinexpensively protected against large transient voltages.

3,334,241 Patented Aug. 1, 1967 In accordance with a feature of theinvention, a zener diode is connected between the emitter electrode ofthe transistor of the amplifier stage and the emitter electrode of thepnp regulating transistor to stabilize the amplifier and hence theregulating transistor, against variations of the input source. The zenerdiode also protects the emitter-base and collector-emitter paths of theregulating and amplifying transistors, respectively, against hightransient voltages. In addition, the zener diode, in combination withthe constant reference zener diode voltage of the error detecting stage,also protects the baseemitter and emitter-collector paths of theamplifying and error detecting transistors, respectively, against highvoltage transients.

Other objects and features of the present invention will become apparentupon consideration of the following detailed description when taken inconnection with the accompanying drawing in which the single figure is aschematic diagram of an embodiment of the invention.

As can be seen from the drawing, two negative line regulators areprovided and, since the regulators are identical, the components of eachregulator are represented by the same reference numbers with primesadded to the reference numbers of the lower regulator. Except whereindicated otherwise, an unprimed numerical designation refers to bothregulators. In each of the regulators the following connections aremade: An input alternating-current source 1 is connected to the primarywinding 2 of transformer 3. The secondary winding 4 of transformer 3 isconnected to the input terminals of full-Wave bridge rectifier 5, whilethe positive and negative output terminals of the bridge rectifier areserially connected with the load 6 and the emitter-collector path ofp-n-p regulating transistor 7. Filter capacitor 8 is also connectedacross the output terminals of the bridge rectifier. Zener diode 9 isserially connected in the zener direction with loading resistor 10 fromthe emitter electrode to the collector electrode of transistor 7. Thecollector-emitter path of n-pn transistor 11 is serially connected fromthe base electrode of transistor 7 to the common terminal of zener diode9 and resistor 10. Resistor 12 is serially connected with theemitter-collector path of p-n-p error detecting transistor 13 from thepositive terminal of bridge rectifier 5 to the base electrode oftransistor 11. Zener diode 14 is connected in the zener direction fromthe emitter electrode of transistor 13 to the emitter electrode ofregulating transistor 7. The end terminals of potentiometer 15 areconnected across the load 6 while the wiper arm of potentiometer 15 isconnected to the base electrode of transistor 13. An output filtercapacitor 18 is connected across the load 6.

The positive terminal of the load 6 of the upper regu-- lator 16 isconnected to the negative terminal of the load 6 of the lower regulator17. The common positive bridge input terminal, and the positive terminalof the load 6', of lower regulator 17 are grounded. Two negative lineregulators, each of which supply a separate load, are shown in thedrawing to illustrate an application wherein high transient voltagesmight be expected. As discussed hereinafter, one such application mightbe found in traveling wave tube circuits where the grid of the tube orthe load 6 of regulator 16 is at one voltage while the second grid ofthe tube or the load 6' of regulator 17 is at a second, lower voltagewith respect to the cathode of the tube or a common point, which may begrounded.

The present invention can best be understood by briefly discussing theregulator circuits of the prior art. Because p-n-p transistors with highpower capabilities are readily available commercially, they are usuallyused as the variable impedance elements in series regulators, i.e.,regulators where the regulating element is serially connected betweenthe source and the load. Series regulators are in turn broken down intotwo classes, namely, positive and negative line regulators, i.e.,regulators wherein the regulating transistor is connected either betweenthe positive input source terminal and the positive terminal of the loador between the negative load terminal and the negative input sourceterminal.

For most practical applications, each of the positive and negative lineregulators usually employ a minimum of three stages, namely, an errordetecting stage which detects variations of the load voltage from areference volt-age, an amplifying stage which amplifies the error signalreceived from the error detecting stage, and the series regulatingstage, the impedance of which is varied under control of the errordetecting stage. The amplifying stage usually has a large loadingresistor connected to it which, in the usual case of the positive lineregulator, is also connected to the positive input terminal to obtainthe proper biasing polarity to the amplifier stage. Since the baseelectrode of the regulating p-n-p transistor is also connected to theamplifier and the emitter electrode is also connected to the positiveinput terminal, the-amplifier loading resistor is thus normally shuntedacross the baseemitter path of the regulating transistor. Recalling thatthe emitter-base path of the regulating p-n-p transistor is essentiallya diode with a relatively low forward conductivity impedance, it isreadily seen that this low impedance will effectively bypass any inputvoltage variations that appear across the loading resistor. Since theinput variations are thus bypassed, the effect of the input variationson the amplifier is negligible, and the circuit remains stable in theevent of such variations. It should perhaps be noted at this point thatany instability due to input variations would have the effect ofdistorting the amplified error signal and thus impair the regulatingproperties of the circuit.

In a negative line regulator, however, the base-collector path of ap-n-p regulating transistor faces the input source and, since this pathexhibits a relatively high impedance, input variations will appearacross both the base-collector path of the regulating transistor and theamplifier load resistor which is connected across the base-collectorpath. The input variations on the amplifier loading resistor introduceinstability in the amplifier and generally distort the error signal tothe point where only poor regulation can be obtained.

To eliminate this problem, many prior art circuits use n-p-n transistorsas the negative line regulating element, in which event the base-emitterpath of the regulating transistor faces the input source and, in themanner discussed in connection with the positive line regulators usingp-n-p transistors, the problem is alleviated. Since n-p-n transistorswith sufficient power capabilities have only limited commercialavailability, however, this variation is usually not satisfactory formost regulator applications, i.e., applications where other than arelatively low power is required.

With this background then, the present circuit is a negative lineregulator employing a p-n-p transistor 7, the base-collector path ofwhich faces the input source, as the regulating element. Error detectingtransistor 13 compares a portion of the load voltage with the constantreference voltage appearing across zener diode 14, which is continuouslyconducting in the inverse or zener direction, and delivers an errorsignal to the amplifier stage n-p-n transistor 11. The amplified signalis, in turn, fed to the base-emitter path of p-n-p regulating transistor7, the impedance of which is thus varied in accordance with load voltagevariations. Resistor 10, which connects the emitter electrode oftransistor 11 to the negative input terminal, serves as the loadingresistor for the amplifier stage.

The manner in which stabilization against input voltage variations isachieved in the present invention is easily seen by examining the effectof input voltage variations on the base-emitter path of regulatingtransistor 7. The

emitter electrode of transistor 7 is connected to the negative terminalof the load 6. Since the voltage appearing across the load 6 isregulated by transistor 7 under control of the feedback loop comprisingerror-detector 13 and amplifier 11, the load voltage, and hence thevoltage appearing at the emitter electrode of transistor 7, is regulatedand hence constant with respect to input voltage variations. The voltageapplied to the base electrode of transistor 7 is the sum of theamplified error voltage appearing across the collector-emitterelectrodes of amplifier transistor 11 and the constant voltage appearingacross zener diode 9. The voltage across the collector-emitter path oftransistor 11 is in turn proportional to the base-emitter voltage oftransistor 11, the latter of which may be easily determined by summingthe voltages in the base-emitter loop. The following loop equation isthus obtained:

where the subscripts b, c, and e refer to the base, collector andemitter electrodes, respectively, the subscript 2 refers to zenervoltage, and the numerals correspond to the numerical designations ofthe components indicated on the drawing. Since V and V or the voltageacross zener diodes 9 and 14, respectively, are constant, the variablecomponent of the voltage appearing across the base-emitter path oftransistor 11 is equal only to the variable voltage component appearingacross the collector-emitter path of error detecting transistor 13.Moreover, as discussed heretofore, the voltage across the load 6 isregulated against input voltage variations, hence only load or errorvoltage variations, due to changes in load, will be reflected by thecollector-emitter voltage of transistor 13. The base-emitter path, andhence the collectoremitter path, of amplifying transistor 11 is thusresponsive only to error voltage variations and is nonresponsive toinput voltage variations. It follows from the previous discussion,therefore, that the base-emitter path of regulating transistor 7 isresponsive only to amplified error voltage variations due to changes inload and is nonresponsive to input variations. The voltage across theload 6 is, therefore, not affected by input voltage variations. Inputvoltage variations are absorbed by resistor 10 without interfering withthe regulating properties of the circuit.

In addition to the stability advantage obtained by the presentinvention, transistor protection advantages are also obtained insituations where it is desired to supply two or more loads, with theloads being referenced to a common point. Such a situation would arise,for example, where it was desired to supply a first voltage of onemagnitude to a grid of a traveling wave tube and a second voltage, of ahigher or lower magnitude with respect to the first voltage, to a secondgrid of the traveling wave tube, with both voltages being referenced toa common point, such as the cathode of the tube. As illustrated by thedrawing in such an application, the negative terminal of the load 6 ofregulator 16 would be connected to the first grid, the common positiveterminal of regulator 16 and the negative terminal of load 6' ofregulator 17 would be connected to the second grid, and the cathode ofthe tube would be grounded as is the positive terminal of regulator 17.Such a configuration could also be used, of course, when it is desiredto supply any two loads, particularly where one is off ground.

With such configurations care must be taken to prevent transistor damagedue to large transients, the magnitudes of which are frequently equalto, or greater than, the potential from the most negative point in thecircuit to ground. Transient voltages of these magnitudes, which aregenerally in excess of the more usual maximum emitter-collector andemitter-base inverse voltage ratings of transistors, may destroy one ormore of the regulator transistors. This is especially true in the caseof high voltage supplies employing the aforenoted combination ofregulators wherein the starting transient voltages are quite large. Theprior art has long recognized this transient problem but, since noapparent alternatives were available, merely chose relatively expensivetransistors with inverse voltage ratings sufficient to withstand thelargest transient voltages anticipated. The present circuit, in additionto the stability and degeneration prevention features noted heretofore,protects the regulator circuit from large transient voltages.Additionally, the network comprising zener diode 9 and resistor 10 willbypass transient current surges around the emitter-collector path oftransistor 7. As noted, zener diode 9 limits the inverse emitter-basevoltage of transistor 7 and the emitter-collector voltage of'transistor11. This limiting and protection action can be easily seen by tracingthe protection path from the positive terminal of diode 9, through theemitter-base path of transistor 7, through the collector-emitter path oftransistor 11, and back to the negative terminal of zener diode 9. Thevoltage across the emitter-base path of transistor 7 and thecollector-emitter path of transistor 11 is thus limited to the zenervoltage of diode 9. Transistor 11, therefore, may be a relativelyinexpensive n-p-n transistor instead of an expensive transistor capableof withstanding high inverse voltages as heretofore thought to benecessary. This is especially important in, although clearly notrestricted to, a situation where two regulators are employed and largetransients might be expected, as in the configurations illustrated inthe drawing. Moreover, the base-emitter path of transistor 11 and theemittercollector path of transistor 13 are also protected by thecomposite limiting action of zener diodes 9 and 14. This is easily seenby tracing the path from the emitter-collector path of transistor 13,through the base-emitter path of transistor 11, through zener diodes 9and 14, and back to the emitter electrode of transistor 13. The sum ofthe voltages appearing across the base-emitter path of transistor 11 andthe emitter-collector path of transistor 13 is thus limited to the sumof the zener voltages of diodes 9 and 14. If desired, a zener diode,poled in the direction of zener diode 9, may be connected across theemitter-col lector path of regulating transistor 7 to protect thistransistor. As discussed heretofore, transistors 11 and 13 may thereforebe inexpensive transistors with relatively low maximum inverse voltageratings rather than the expensive high inverse voltage rated transistorsheretofore thought to be necessary.

In summary, therefore, a zener diode 9 connects the emitter electrode ofamplifying transistor 11 to the emitter electrode of the regulatingtransistor 7 to prevent instability or degeneration due to input voltagevariations. The stability against input voltage variations is readilyseen once it is noted that since the load voltage is regulated, it willvary only with changes in load, and the voltage at the emitter electrodeof regulating transistor 7 is therefore nonresponsive to input voltagevariations. The volt-age at the base electrode of transistor 7 is equalto the sum of the collector-emitter voltage of transistor 11 and thevoltage across zener diode 9, the latter which is continuouslyconducting in the inverse or zener direction. The collector-emittervoltage of transistor 11 is in turn proportional to its base-emittervolt age, the latter of which may be easily determined by summing thevoltages in the base-emitter loop. The voltages in this loop compriseonly the voltages across diodes 9 and 14, which are continuouslyconducting in the inverse direction and hence have a constant voltagedrop across them, and the voltage across the emittercollector path oferror detecting transistor 13. Since transistor 13 is connected to theload or regulated side of the regulating transistor 7, it is responsiveonly to load voltage variations and is nonresponsive to inputvariations. The collector-emitter voltage drop of transistor 13 istherefore nonresponsive to input variations and, since it is the onlyvariable voltage in the loop in which the base-emitter path ofamplifying transistor 11 -is connected, transistor 11 must thereforealso be nonresponsive to input voltage variations. As noted heretofore,transistor 11 in turn directly drives the baseemitter path of regulatingtransistor 7 which must therefore also be nonresponsive to input voltagevariations.

In addition to the stability and degeneration prevention features, zenerdiode 9 also limits the maximum inverse transient voltages appearingacross the emitter-base path of transistor 7 and the collector-emitterpath of transisor 11. The composite effect of zener diodes 9 and 14 isto limit the maximum inverse transient voltages appearing across thebase-emitter path of transistor 11 and the collector-emitter path oftransistor 14. The regulator circuits are thus readily applicable tosituations wherein it is desired to provide output voltages at differentmagnitudes with respect to a common point.

The above-described arrangement is illustrative of the principles of theinvention. Other embodiments may be devised by those skilled in the artwithout departing from the spirit and scope of the invention.

What is claimed is:

1. A regulator comprising a source of input voltage, a load, regulatingand amplifying transistors, each having base, collector, and emitterelectrodes, means serially connecting said source of input voltage, saidload, and the emitter-collector path of said regulating transistor, theemitter electrode of said regulating transistor being connected to saidload, the collector electrode of said regulating transistor beingconnected to said source, detecting means responsive to variations ofsaid load voltage from a reference voltage, means connecting thebase-emitter path of said amplifying transistor to receive currentvariations from said detecting means, means connecting thecollector-emitter path of said amplifying transistor to supply currentto the emitter-base path of said regulating transistor, and biasingstabilization means connected to the emitter electrodes of saidregulating and amplifying transistors to maintain a substantiallyconstant voltage independent of input source variations between theemitter electrodes of said regulating and amplifying transistors,whereby the regulating function of the emitter-collector path of saidregulating transistor is made insensitive to amplitude variations ofsaid input source.

2. A regulator comprising a source of input voltage, a load, regulatingand amplifying transistors, each having base, collector, and emitterelectrodes, means serially connecting said source of input voltage, saidload, and the emitter-collector path of said regulating transistor, theemitter electrode of said regulating transistor being connected to saidload, the collector electrode of said regulating transistor beingconnected to said source, detecting means responsive to variations ofsaid load voltage from a reference voltage, means connecting thebaseemitter path of said amplifying transistor to receive currentvariations from said detecting means, and normally conductive biasingstabilization means serially connecting the emitter-collector path ofsaid amplifying transistor and the base-emitter path of said regulatingtransistor to supply current from said amplifying transistor to saidregulating transistor and to stabilize the voltage appearing across saidemitter-collector and said base-emitter paths of said amplifying andregulating transistors at a predetermined magnitude whereby saidregulating and said amplifying transistors are protected from highinverse voltage transients above said predetermined magnitude.

3. A regulator comprising a source of input voltage, a

load, regulating and amplifying transistors, each having path of saidamplifying transistor to receive current variations from said detectingmeans, means connecting the collector-emitter path of said amplifyingtransistor to supply current to the emitter-base path of said regulatingtransistor, a zener diode, said zener diode being connected between theemitter electrodes of said regulating and amplifying transistors so asto be continuously conducting in the inverse direction to maintain asubstantially constant potential difference between the emitterelectrodes of said regulating and amplifying transistors whereby theregulating function of the emitter-collector path of said regulatingtransistor is insensitive to amplitude variations of said input source.

4. A regulator comprising a source of input voltage, a load, regulatingand amplifying transistors, each having base, collector, and emitterelectrodes, means serially connecting said source of input voltage, saidload, and the emitter-collector path of said regulating transistor, theemitter electrode of said regulating transistor being connected to saidload, the collector electrode of said regulating transistor beingconnected to said source, detecting means responsive to variations ofsaid load voltage from a reference voltage, means connecting thebase-emitter path of said amplifying transistor to receive currentvariations from said detecting means, means connecting thecollector-emitter path of said amplifying transistor to supply currentto the emitter-base path of said regulating transistor, an amplifierloading resistor connected between the emitter electrode of saidamplifying transistor and the terminal of said input source to which thecollector electrode of said regulating transistor is connected, and azener diode connected in the zener direction from the emitter electrodeof said regulating transistor to the emitter electrode of saidamplifying transistor to maintain a substantially constant potentialinsensitive to input voltage variations across said loading resistorbetween the emitter electrodes of said regulating and amplifyingtransistors, whereby input source variations all appear across saidloading resistor without interfering with the regulating properties ofthe regulator.

5. A negative line regulator comprising a source of input potential, aload, a regulating transistor, an amplifying transistor, and an errordetecting transistor, each of said transistors having base, collector,and emitter electrodes, means serially connecting said source of inputpotential, said load, and the emitter-collector path of said regulatingtransistor, means connecting the base-emitter path of said errordetecting transistor to a constant reference voltage and at least aportion of the voltage appearing across said load to detect variationsof the load voltage from the constant reference voltage, meansconnecting the emitter-collector path of said error detecting transistorto the base-emitter path of said amplifying trans-istor, an amplifyingtransistor, a loading resistor, a zener diode, means connecting saidloading resistor from the emitter electrode of said amplifyingtransistor to the collector electrode of said regulating transistor,means connecting the collector electrode of said amplifying transistorto the base electrode of said regulating transistor to control saidregulating transistor in accordance with load voltage variations, andmeans serially connecting said loading resistor and said zener diodeacross the emitter-collector path of said regulating transistor suchthat said zener diode is continuously conductive in the inversedirection to stabilize the potential appearing at the emitter electrodesof said amplifying and regulating transistors and to protect said errordetecting, amplifying, and regulating transistors from high inversetransient voltages.

6. A power supply comprising first and second negative line regulators,each of said regulators having an individual source of input potential,an individual load, and individual regulating and amplifyingtransistors, each of said transistors having base, collector, andemitter electrodes, means in each of said first and second regulatorsserially connecting said source of input potential, said load, and theemitter-collector path of said regulating transistor, the emitterelectrode of said regulating transistor being connected to said load,the collector electrode of said transistor being connected to saidsource, detect-ing means in each of said first and second regulatorsresponsive to variations of load voltage from a reference voltage, meansin each of said first and second regulators connecting the base-emitterpath of said amplifying transistor to said detecting means to receivecurrent variations from said detecting means, an amplifier loadingresistor in each of said first and second regulators connected betweenthe emitter electrode of said amplifying transistor and the collectorelectrode of said regulating transistor in each of said first and secondregulators, means connect-ing one terminal of the load of said firstregulator to one terminal of the load of said second regulator, means ineach of said first and second regulators connecting thecollector-emitter path of said amplifying transistor to supply currentto the base-emitter path of said regulating transistor, and a zenerdiode connected in the zener direction from the emitter electrode ofsaid regulating transistor to the emitter electrode of said amplifyingtransistor in each of said first and second regulators to maintain asubstantially constant voltage insensitive to input or transient voltagevariations across said loading resistor between the emitter electrodesof said regulating transistors, whereby the transistors in each of saidfirst and second regulators are also protected from transients in excessof the sum of the voltages appearing across said loads in said first andsecond regulators.

References Cited UNITED STATES PATENTS 2,693,568 11/1954 Chase 32l182,751,549 6/1956 Chase 321-18 2,904,742 9/1959 Chase 3239 X 2,917,70012/1959 Chase 32322 3,106,674 10/1963 Hamilton 32118 X 3,185,856 5/1965Harrison 30755 ORIS L. MDER, Primary Examiner.

T, J. MADDEN, Assistant Examiner,

1. A REGULATOR COMPRISING A SOURCE OF INPUT VOLTAGE, A LOAD, REGULATINGAND AMPLIFYING TRANSISTORS, EACH HAVING BASE, COLLECTOR, AND EMITTERELECTRODES, MEANS SERIALLY CONNECTING SAID SOURCE OF INPUT VOLTAGE, SAIDLOAD, AND THE EMITTER-COLLECTOR PATH OF SAID REGULATING TRANSISTOR, THEEMITTER ELECTRODE OF SAID REGULATING TRANSISTOR BEING CONNECTED TO SAIDLOAD, THE COLLECTOR ELECTRODE OF SAID REGULATING TRANSISTOR BEINGCONNECTED TO SAID SOURCE, DETECTING MEANS RESPONSIVE TO VARATIONS OFSAID LOAD VOLTAGE FROM A REFERENCE VOLTAGE, MEANS CONNECTING THEBASE-EMITTER PATH OF SAID AMPLIFYING TRANSISTOR TO RECEIVE CURRENTVARIATIONS FROM SAID DETECTING MEANS, MEANS CONNECTING THECOLLECTOR-EMITTER PATH OF SAID AMPLIFYING TRANSISTOR TO SUPPLY CURRENTTO THE EMITTER-BASE PATH OF SAID REGULATING TRANSISTOR, AND BIASINGSTABILIZATION MEANS CONNECTED TO THE EMITTER ELECTRODES OF SAIDREGULATING AND AMPLIFYING TRANSISTORS TO MAINTAIN A SUBSTANTIALLYCONSTANT VOLTAGE INDEPENDENT OF INPUT SOURCE VARIATIONS BETWEEN THEEMITTER ELECTRODES OF SAID REGULATING AND AMPLIFYING TRANSISTORS,WHEREBY THE REGULATING FUNCTION OF THE EMITTER-COLLECTOR PATH OF SAIDREGULATING TRANSISTOR IS MADE INSENSITIVE TO AMPLITUDE VARIATIONS OFSAID INPUT SOURCE.